Power factor correction (PFC) circuitry is typically added at an input side of a converter to decrease harmonic pollution to the power grid generated by power electric apparatuses. Active PFC may be utilized to increase the power factor of power electric apparatuses to decrease harmonic pollution because the input current can be regulated to be in phase with input voltage. Boost PFC topology is typically used to act as an active PFC circuit, which may become more attractive to high power applications in continuous conduction mode (CCM). A typical CCM boost PFC circuit will be described with reference to the example of FIG. 1.
In FIG. 1, shown is a schematic diagram of a conventional CCM boost PFC circuit including a power stage and a control circuit. The power stage can include inductor L, power switch SM, diode D, input capacitor Cin, and output capacitor Cout, to form a boost topology. Average current control mode may be utilized by the control circuit that can include a current loop and a voltage loop. Inductor current can be detected by inductor current sensing circuit 101, and averaged to generate sensing voltage signal Vsen representative of the average of the inductor current. Multiplier 102 can receive rectified input voltage Vg and feedback signal Vc, generated by output voltage feedback circuit 103, to generate reference signal Vr. Error amplifier W1 may be used to calculate and amplify the error between reference signal Vr and sensing voltage signal Vsen to generate error signal Ve. The PWM control circuit may be used to generate a control signal for operation of power switch SM in based on error signal Ve and a sawtooth signal, as shown. Input current may be regulated accordingly to maintain an input current waveform that follows the input voltage to achieve power factor correction.
For this conventional CCM boost PFC circuit, the switching frequency of power switch SM is constant as determined by an inner clock signal, such as the sawtooth signal generated by an oscillator. To achieve improved electromagnetic interference (EMI) performance, a frequency jitter technique may be used to isolate higher frequency range noise.